Now that was an easy one, since it can be broken down into blinkers and eaters. The question here is how to synthesise other oscillators that aren't that simple, like 24P10 or 48P31. There are two main problems here: (1) how to derive a predecessor of the rotor comprised of still lifes and sparks and (2) how to provide these sparks. After that, assembling the actual synthesis should be easy.

All that's missing is a suitably placed domino spark (presumably known), and a suitable reaction to generate the preblock (unknown). Then we will have 18P2.420 synthesized.

If the particular preblock synthesis doesn't work out, we can always try starting from gen. 117 of the rightmost section of that pattern. However, I do not currently know how to adequately synthesize that preblinker. (The synthesis I posted requires a collision between a glider and something moving, at about c/2, to the left.)

(BTW, the only way I know of to generate the preblock occurs in the LOM reaction. A ghosted Herschel could also work, if we could modify it somewhat.)

I recently tried to make sure I had syntheses for all of the objects in Achim Flammenkamp's "natural objects" lists. I ended up having to create new syntheses for several new ones; the hardest ones were some of the largest P2s. I currently have all except one - Fore and Back. 18P2.420 is one of these, and is totally buildable from existing technology.

Here are the ones I saw on Achim's list that are in the Wiki but I didn't see syntheses for:

Extrementhusiast wrote:Well, if we had soups containing it, perhaps something similar to what was done with Coe's P8 could be done.

And with the synthesis of the eater3, oscillators containing that are now one step closer to being synthesized.

Many of the oscillators containing eater-3 are based on shuttling pairs of gliders. Unfortunately, this particular stator arrangement doesn't work for those, as it gets too close to one of the gliders.

mniemiec wrote:I recently tried to make sure I had syntheses for all of the objects in Achim Flammenkamp's "natural objects" lists. I ended up having to create new syntheses for several new ones; the hardest ones were some of the largest P2s. I currently have all except one - Fore and Back.

Here's a 20x20 soup which produces a Fore + Back; maybe a synthesis could be worked out from this? (Sorry about the file type not being RLE, I'm stuck without any proper life programs for a few days until I get a new computer. It should still copy/paste into Golly though).

Extrementhusiast wrote:EDIT: The synthesis itself:...This could most likely be improved.

Congratulations on the Fore and Back synthesis! I had been expecting it to come from a symmetrical predecessor, so I was surprised at the immediate predecessor shown here. I tried to create another way to synthesize that predecessor directly and more cheaply, but it was ultimately unrewarding. Basically, starting from a 3-part still-life (that would likely take 10-12 gliders to create), and then activating it with 12 additional gliders - and that only made everything except the top block (which was impossible to add), which would have cost than the original synthesis itself, so it wasn't worth it.

However, 15 generations after this (2 generations before the Fore and Back actually forms), the predessor resembles a round object whose two sides are mutilated in different ways. It turns out that either kind of mutilation can be done on both sides simultaneously, i.e. from a symmetrical predecessor. The top one can be accomplished by adding a simple domino spark. The central symmetrical object itself seems fairly common, and turns into a tub. There just happens to be a 4-glider tub synthesis (i.e. from two adjacent boats) that makes it using this very predecessor, which makes a good starting point. Unfortunately, adding the required spark takes some work (8 glider per side), so it takes 20 gliders to put it all together, only a slight improvment on the original:

This should be reducible further, probably to 16 gliders. They key catalyst occurs at generation 14. Ideally, a domino spark with a bit-spark form the required domino in one step. Here, the bit-spark is replaced by another domino, making a blinker instead. This affects the predecessor in a slightly different way, but ends up with the same result. It should theoretically be possible to make the outside domino from 3 gliders rather than 5, but I couldn't find it.

Extrementhusiast wrote:Oddly enough, the improvement may be on the inside, rather than the outside. I noticed that a single-bit spark would do the job, as well as the domino spark that was used.

Also, I noticed this:...

That's what I meant. The desired catalyst at generation 15 is a single domino, but getting that domino there is not possible directly. A domino one further west at generation 14, plus a single bit a knight's-move southeast of it allow the domino to be pulled west one space in the next generation. I couldn't get that bit spark there, but I found that a domino instead (as shown) was feasible, and makes a blinker at 14 instead. This attacks the core differently, but ends up with the same result.

Interesting similarity between the double cuphook and the P9. I'll have to have a closer look to see if one is easy to build (and, if so, how hard it would be to change into the other).

Add the indicated domino spark between gens. 2-6. (With gen. 2, you have to change the block up a bit.) Also, if there were any ways to extend the top end of the inductor by one bit for one generation, those could be used instead of the block.

I lost the hosting on my web site (with tons of syntheses) earlier this year. I plan to eventually put it up again, but meanwhile, I've been adding about a decade worth of changes and improvements to it before doing so - the last update was in Nov. 1999! I've also been trying to synthesize a lot of objects that I've found on the wiki and elsewhere - such as the few I've posted here recently. (In perspective, the old site had around 3800 syntheses, and the new updated one has around 10,000, most of which are trivial, but many are not.) It's getting close to being ready for prime time. One thing I still need to do is to look at all the syntheses from the wiki to see what I have that's been subsequently improved. (I've downloaded all of them, but only looked at some so far).

There was one component where an 11.12 was turned into a 12.34. I know it took about ten gliders, and involved an eater, but for the life of me, I can't remember it. Do you know what it was? It went something like this:

48p31 is very intriguing: it looks like it's made up of all simple parts, yet the key component (loaf with attached diagonal bit) is somewhat problematic, in that it's not nearly as "natural" as one would hope. Attaching such a bit to a single loaf is easy, but requires scaffolding that is too large to be sandwiched between two loaves.

This CAN be done easily, if the loaf and the bit appear simultaneously, for example, by flipping the loaf into place with a glider. Again, this is trivial to do for one loaf, but much more difficult for two nearby loaves simultaneously.

After much hair-pulling, I figured out a way to do this by brute force, with a horrid Rube-Goldberg contraption, using a block-on-eater-on-eater, but there was so much going on that it was only possible to bring in one pair of stabilizing blocks, but not the other. I was, however, able to re-work it using 11.34s instead of eaters.

I think you meant "Merzy's p31 from 68 gliders", not 72. You accidentally included two blinkers (four gliders) into the count, which don't play a part in the synthesis at all. I understand that the raw count gives 66, but a four-glider synthesis is required for two of the four LWSSs due to proximity reasons.